This invention relates to a spool-sleeve type change-over valve, and more particularly to a spool-sleeve type change-over valve which is provided with fluid intake and discharge passages of particular dimensions to attain a high cylinder response at a given stroke length of the spool or to attain a given cylinder response at a shorter stroke length.
Spool-sleeve type change-over valves generally consist of a casing having a fluid intake port, first and second output ports located on the opposite sides of the fluid intake port and first and second discharge ports located on the outer sides of the respective output ports, a sleeve fixedly fitted in the casing to define a cylindrical valve chamber and having rows of circumferentially aligned apertures, including intake apertures, output apertures and discharge apertures, respectively in open communication with the intake, output and discharge ports in the casing, and a spool slidably fitted in a cylindrical valve chamber and having lands slidable across the intake and discharge apertures of the sleeve to switch the fluid flows.
In this type of change-over valve, the intake and discharge apertures of the sleeve which communicate with the intake and discharge ports in the casing are usually formed to have equal widths in the axial direction of the sleeve and the spool is operated through a stroke length corresponding to the width of the intake apertures plus the width of the discharge apertures.
However, as a result of exhaustive experiments on the relationship between the open widths of the respective apertures and the response velocity of the working cylinders which are connected to the output ports, it has been found that under light load conditions the cylinder response is primarily governed by the effective sectional area of the discharge passage rather than that of the intake passage, and that there is a certain range in which the effective sectional area of the intake passage can be reduced relative to that of the discharge passage without lowering the cylinder response as compared with the velocity which would be obtained by the use of intake and discharge passages of the same effective sectional areas.